I shot a model awhile ago but we had a falling out before i was able to get a release of any sort from her.
I love one of the pieces and would like to use it in my personal collection for a gallery. It would be untitled and not for sale and there's no nudity or offensive material. I'd like to know - as a photographer am i protected legally in doing this?

How an image was made and how it will be used determine if a model release is needed.

A model release protects the interests of 2 parties:

the model

the publisher

Notice the photographer is not even mentioned, however sometimes the photographer becomes the publisher of an image.

At this point the question then hinges on: What constitutes publishing?

Personal use, is not publishing. But, you also need to be aware there are 2 kinds of publishing:

Commercial

Editorial

Understanding the differences is not an easy task.

There are also considerations for self-publishing and self-promotion.

I recommend you get the book: A Digital Photographers Guide to Model Releases by Dan Heller

You can visit Model Release Primer and get a less detailed version that may, or may not answer your questions.

Be aware that model release requirements and 'right of publicity' laws vary by state.

At any rate - seeking legal advice in online discussion forums is not recommended since there is a TON of legal urban legend floating around, so you really should consult with an attornet familiar with this sub-specialty of law (publishing and releases).